Battery replaced with iFixit kit but doesn’t appear to charge.

Hi, I finally had the courage to gut open the iPad Air 2 that still had an original but dead apple battery.

I followed the instructions on the website, it wasn’t hard but it was just time consuming. The charger is connected but no sign of life. The screen remains black. Does it take a long time to charge and boot for the first time ? How can I troubleshoot and find out if I broke something or if the new battery is defective?

edit: I didn’t remove the adhesive of the back of the battery nor replaced the ones around the bezels for testing purposes for fairly obvious reasons.